Abstract: This system is formed, on the one hand, by a transmitting section (1) comprising coders (CA, CB, CC) for coding according to an error detection code the data to be transmitted over the main channels and comprising a coder (CS) for an auxiliary channel (CHS) and, on the other hand, a receiving section (2) constituted by error detecting circuits (DA, DB, DC, DS). In the transmitting section there is provided a combining circuit (20) for combining the data to be transmitted over the main channels, whereas the auxiliary channel is used for transmitting the combined data. In the receiving section there are provided decombining circuits (USA, USB, USC) for producing replicas of the transmitted data for each of the main transmission channels on the basis of data transmitted over the auxiliary channel. These replicas are used in case of failing transmission channels.

Abstract: A baseband-controlled passband equalizing arrangement comprises a passband correction circuit for the data signals transmitted by modulating a carrier frequency, a first demodulation circuit which cooperates with a carrier recovery circuit for converting these carrier-modulated data signals into baseband signals, and a control circuit acting on the variable elements provided in the passband correction circuit in response to an estimated error of the baseband signals. The passband correction circuit produces a passband output signal v(t), which is a continuous function of the time t, in response to a passband input signal x(t), which is a continuous function of the time t, in accordance with the relation: ##EQU1## where r.sub.m, .psi..sub.m, .rho..sub.j, .phi..sub.j are variable elements, and .tau..sub.j, .tau..sub.m are fixed delays and M, N are constants.

Abstract: Apparatus for controlling the transmission power of a transmitting station over a digital radio communication channel, based on information relating to the level of the signal received at a receiving station and information relating to the quality of such received signal relative to a predetermined error rate. The signal level information and signal quality information is derived by respective threshold measurement devices in the receiving station, and is transmitted back to the transmitting station over a return channel. The transmitting station comprises means for effecting combined processing of such information to derive a control signal which controls means for increasing or decreasing the transmitting power over a dynamic adjustment range. In a first part of such dynamic range such control is based only on the information relating to received signal level, and over a second part of such range such control is additionally based on the quality of the received signal.

Abstract: An adaptive equalizer arrangement for digital transmission system comprises at the output of the transmission channel a first in-phase path and in parallel with this first path, a second quadrature path, both paths being of the non-recursive transversal filter type having n branches and (n-1) delay circuits between the inputs of these branches, each of these n branches comprising, arranged in series, a mixer, a low-pass filter, a multiplier, and having their outputs connected to an adder which is followed by a sampling circuit and thereafter by a comparator circuit to decide the symbols to be transmitted from the outputs of these paths. The arrangement also comprises a third control path which comprises two subtracting circuits to determine the differences between the signals before and after decision and a control circuit of a voltage-controlled oscillator, 2n phase shifters and 2n multipliers.

Abstract: A circuit for recovering the carrier of an amplitude-and-phase-modulated input signal (in particular QAM signal) is provided with a frequency-controlled oscillator for producing the carrier, with a quadrature detector for supplying signals representing the amplitude of the input signal projected on two quadrature components P and Q of the carrier signal produced by the oscillator and for thus determining the modulation states of the input signal, and with correction means for forming a correction signal for the frequency control of the oscillator on the basis of output signals from a circuit which determines zones in the plane of the quadrature components P and Q. To provide for a satisfactory operation also in the presence of selective fading, the correction means comprises a weighting circuit connected to the zone-determining circuit for producing the correction signal in accordance with distinct weights allocated to the respective zones defined by the zone-determining circuit.

Abstract: In this transmission system using differential PCM, the local decoder, inporated in the loop of the encoder, and the remote decoder comprise identical filters (5) and (15) each constituted by a cascade arrangement of several filtering sections (F.sub.1 -F.sub.N) of the first and/or of the second order; each section may have one or two controllable coefficients, which are modified at each sampling instant by a modification term which depends upon the product of the difference signal (e) produced in the encoder and the gradient of the difference signal (e) with respect to the controllable coefficient. When the filtering sections (F.sub.1 -F.sub.N) are recursive, the gradients are obtained by applying a signal corresponding to the difference signal (e) to identical recursive sections (F'.sub.1 -F'.sub.N). When non-recursive filtering sections (H.sub.1 -H.sub.L) are used, the gradient calculation sections (H'.sub.1 -H'.sub.L) are recursive with a transfer function inverse to that of the sections (H.sub.1 -H.sub.

Abstract: This system comprises an encoder in which the differential PCM signal to be transmitted is formed as the difference between the incoming linear PCM signal and a prediction signal produced by a prediction filter comprising a local decoder receiving the said differential PCM signal. According to the invention the local decoder and the remote decoder are constructed in an identical manner by means of one or several filtering sections arranged in cascade, each filtering section being of the purely recursive or non-recursive type with one sole coefficient differing from zero and having been provided with its own roundoff (or truncation) device having a step size equal to the quantizing step of the differential PCM signal, the incoming linear PCM signal being rounded (or truncated) in the same manner. This construction enables the cascade arrangement of encoders and decoders without any further degradation of the signal then the degradation produced by the first coding.

Abstract: To supervise the operation of an arithmetic unit of a digital transmultiplexer intended to convert a TDM-signal into a FDM-signal and vice versa, a pilot signal is utilized as the test signal which pilot signal is also used to control the level of the received FDM-signals and is processed in the transmultiplexer. The pilot signal selection filter used for controlling the level is used, also in time-division multiplex, for selecting a component having a frequency equal to the pilot signal frequency and occurring in each of the two input and output signals of the arithmetic unit.

Abstract: Level control arrangement for frequency-division multiplex signals, comprising an amplifying device having a variable gain factor, a circuit for transposing the frequency of the multiplex signal at the output of said arrangement in order to bring the frequency of the pilot signal to a low frequency; a low-pass filter for limiting the spectrum of the transposed signal; and analog-to-digital converter in the form of a uniform delta modulator, the input whereof is connected to the output of the low-pass filter. In a code converter this delta modulation signal is converted into either a PCM signal, or a DPCM signal, and the signal thus obtained is applied to a digital filter for selecting a signal which is characteristic of said pilot signal. The filtered signal is applied to a detector for detecting the peak values. The peak values obtained are applied to a comparison device for generating an error signal which sets the value of the gain factor of the amplifying device.

Abstract: A circuit for converting into an FDM format spatially separated signalling signals and pilot signals, comprises a digital filter bank for converting the signals into the FDM format. A receiver for separating the signalling signals and pilot signals from the FDM signal comprises another digital filter bank for producing baseband signals. These filter banks have a transfer characteristic formed by a number of passband curves which are derived from the characteristic of a selected low-pass filter.

Abstract: An arrangement for computing the discrete Fourier transform intended for converting N samples of a real signal in the time domain to N real Fourier coefficients. This device is implemented with a conventional Fourier transformer of the order N/4, to which an input computer unit and an output computer unit are connected in which a small number of multiplications of complex numbers is performed.